1. Field of the Invention
The present invention relates to an organic electro luminescence display device, and more particularly to an organic electro luminescence display device that is adaptive for improving its contrast ratio, and a fabricating method thereof.
2. Description of the Related Art
Recently, there have been developed a variety of flat panel display devices that can reduce their weight and size, which are a disadvantage of a cathode ray tube CRT. The flat panel display device includes a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro luminescence EL display device.
Especially, the EL display device basically has a shape of sticking an electrode to both side surfaces of an organic light emitting layer which is made up of a hole transport layer, a light emitting layer and an electron transport layer, and the EL display device attracts attention as a next generation flat panel display because of its wide viewing angle, high aperture ratio, high color sense and so on.
The EL display device is largely divided into an inorganic EL display device and an organic EL display device in accordance with a material used. The organic EL display device among these has an advantage of being driven with lower voltage than an inorganic EL display device because electrons and holes form pairs and then they become extinct to emit light when electric charges are injected into an organic EL layer which is formed between a hole injection electrode and an electron injection electrode. Further, the organic EL display device can form elements even on a transparent substrate which is flexible like plastics, and the organic EL display device can be driven at a low voltage of below 10V, has relatively low power consumption and has excellent color sense in comparison with the PDP or the inorganic EL display device.
FIG. 1 is a perspective view representing a related art organic EL display device, and FIG. 2 is a diagram representing the organic EL display device shown in FIG. 1, taken along the line I-I′.
The organic EL display device shown in FIG. 1 has a first electrode (or an anode electrode) 4 and a second electrode (or a cathode electrode) 12 formed on a substrate 2 in a direction of crossing each other.
A plurality of anode electrodes 4 are formed on the substrate 2 to be separated from each other with a designated gap. An insulating film 6 having an aperture part for each EL cell area is formed on the substrate 2 where the anode electrode 4 is formed. Barrier ribs 8 are located on the insulating film 6 for separating an organic light emitting layer 10 and the cathode electrode 12 which are to be formed thereon. The barrier ribs 8 are formed in a direction of crossing the anode electrode 4 and have a reverse taper structure where an upper end part has a wider width than a lower end part. The organic light emitting layer 10 and the cathode electrode 12 formed of an organic compound are sequentially deposited over the entire surface of the insulating film 6 where the barrier ribs 8 are formed. The organic light emitting layer 10 has a hole transport layer, a light emitting layer and an electron transport layer deposited and formed on the insulating film. The organic EL display device has electrons and holes emitted if a driving signal is applied to the anode electrode 4 and the cathode electrode 12, and the electrons and holes emitted from the anode electrode 4 and the cathode electrode 12 are recombined within the organic light emitting layer 10 to generate a visible ray. At this moment, the generated visible ray exits to the outside through the anode electrode 4 to display a designated picture or image.
On the other hand, in the related art organic EL display device, the light incident from the outside almost completely transmits the anode electrode 4, the barrier rib 8 and the organic light emitting layer 10. As a result, when the light is not emitted from the organic light emitting layer 10, as shown in FIG. 3, an external light 40 being incident from the surface of the substrate 2 transmits the organic light emitting layer 10 and the anode electrode 4 of a transparent conductive material, and is reflected by the cathode electrode 12 of metal electrode to exit to the outside of the device. Accordingly, there is a problem in that its contrast ratio is deteriorated.